Monolithically integrable semiconductor circuit with an amplifier controlled by a photo diode

Abstract

Monolithically integrable semiconductor circuit with an amplifier controlled by a photo diode, including a differential amplifier having inverting and noninverting inputs and outputs and a photo diode having a first and a second lead, the first lead of the photo diode being connected in the blocking direction to the inverting input of the differential amplifier, and the noninverting input of the differential amplifier being connected to a reference potential, a coupling resistor connected between the inverting and noninverting inputs of the differential amplifier, a filter circuit and a transistor amplifier being connected in a feedback branch between the noninverting output and the inverting input of the differential amplifier, and the inverting output of the differential amplifier and the second lead of the photo diode being connected to ground.

There are claimed: 
     
       1. Monolithically integrable semiconductor circuit with an amplifier controlled by a photo diode, comprising a differential amplifier having inverting and noninverting inputs and outputs and a photo diode having a first and a second lead, the first lead of said photo diode being connected in the blocking direction to the inverting input of said differential amplifier, and the noninverting input of said differential amplifier being connected to a reference potential, a coupling resistor connected between the inverting and noninverting inputs of said differential amplifier, a filter circuit and a transistor amplifier being connected in a feedback branch between the noninverting output and the inverting input of said differential amplifier, and the inverting output of said differential amplifier and the second lead of said photo diode being connected to ground. 
     
     
       2. Circuit according to claim 1 including a resistor connected between the inverting output of said differential amplifier and ground, and a resistor connected between the second lead of said photo diode and ground. 
     
     
       3. Circuit according to claim 1, wherein said filter circuit causes an attenuation in said feedback branch which is greater than the gain of said differential and transistor amplifiers disposed in said branch, for all useful signal frequencies. 
     
     
       4. Circuit according to claim 3, wherein said filter circuit is a lowpass filter. 
     
     
       5. Circuit according to claim 4, wherein said filter is a two-section lowpass filter. 
     
     
       6. Circuit according to claim 3, wherein said filter circuit is a band rejection filter with a rejection frequency corresponding to the transmission frequency. 
     
     
       7. Circuit according to claim 1, including an amplifier circuit, the anode of said photo diode being connected to the output of said amplifier circuit and the cathode of said photo diode being connected to the input of said amplifier circuit. 
     
     
       8. Circuit according to claim 7, wherein said amplifier circuit comprises identical first and second bipolar transistors of a given type, a third bipolar transistor of opposite type to said first and second transistor, a first and second current supply, and a current mirror amplifier, the cathode of said photo diode being connected to the base of said first transistor, the collector of said first transistor being connected to ground, the emitter of said first transistor being connected to said first current supply and to the base of said second transistor, the emitter of said second transistor being connected to said second current supply and to the base of said third transistor, the collector of said third transistor being connected to a control input of said current mirror amplifier, an output of said current mirror amplifier being fed back to the anode of said photo diode, and including a resistor connected between the emitter of said third transistor and the noninverting input of said differential amplifier. 
     
     
       9. Circuit according to claim 8, including an integrated circuit having a substrate and an epitaxial layer, said epitaxial layer containing said photo diode and having a conduction type opposite to that of said substrate, the emitter of said first transistor being connected antiparallel to said photo diode, having the same conduction type as said substrate, and said integrated circuit having no further pn-junction between the pn-junction intermediate said substrate and epitaxial layer and the pn-junction of said photo diode. 
     
     
       10. Circuit according to claim 2, wherein said resistor connected between the second lead of said photo diode and ground has a lower resistance than said coupling resistor.